Kyurem Complete
"The Infinite Grey Pokemon"
Ability - Truth And Ideals: When low on health, Kyurem Complete becomes normal Kyurem and Zekrom and Reshirahm become "sidekicks" like how Totem Pokemon can have "Sidekicks"
Special Moves - Mega Aura: A mist that appears for 5 turns. Any Pokemon that can Mega Evolve regardless of they have a stone or not, on Kyurem's team can Mega Evolve. Can't be used the same time as Suppression Aura. Suppression Aura: A mist for 5 turns that prevents opponents from Mega Evolving
Backstory: Kyurem Complete came from a meteor in space which is why the Giant Chasm is there. Pieces of the meteor scattered all around the world. These meteors are the "Pure Form" of Mega Evolutions before they where irradiated by Xerneas/Yveltal. So basically Kyurem Complete is the ultimate Mega Evolution Pokemon which makes sense since Colress in Black/White 2 was all over trying to find the "full potential" of Pokemon